Micro‐scale, In‐plane Thermal Conductivity of PEDOT:PSS Thin Films Measured by a Suspended Membrane Device

Abstract

The in‐plane thermal conductivity of ultra‐thin films is of high interest due to its role in many technological applications, while being very challenging to measure. The challenge lies in creating a heat flow laterally through the thin sample film while eliminating all heat losses to the substrate and the surrounding air. A technique involving two parallel, line‐shaped resistance temperature detectors (RTDs) as a pair of heater and sensor on a nanometer‐thin suspended membrane, which minimizes heat losses to the substrate, has been recently introduced and numerically modeled. Herein, measurements employing two parallel line RTDs on a (164 ± 3) nm thin silicon nitride (SiNx) membrane for characterization of heat flux in electrically conductive polymer films are presented. On top of heater and RTD, silicon dioxide (SiO2) is used as a electrical passivation layer. (118 ± 35) nm poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) thin films are characterized. The methodology to enable these measurements starting from the fabrication of the devices using photolithography and chemical wet etching and the assembly of the high vacuum setup for precise measurements are discussed. Thermal conductivities of 2.9 ± 0.2 W m−1 K−1, 0.6 ± 0.2 W m−1 K−1, and 0.4 ± 0.8 W m−1 K−1 are measured for the SiNx, SiO2 and PEDOT:PSS thin films, respectively. Our findings can facilitate this flexible measurement method to other material systems.